Blog

Diet quality, environmental impacts, and food waste

A few years ago when the federal dietary guidelines were being discussed, there seemed to be a growing consensus that nutritional goals and sustainable goals could be jointly achieved with a single diet.  I pushed back some on that at the time (e.g., see here or here).

I ran across this paper by Zach Conrad and colleagues that was just published in PLoS ONE.  The paper shows that there is unlikely to be a silver bullet diet free of trade-offs when multiple dimensions of comparison are involved.  Here's from the abstract:  

Higher quality diets were associated with greater amounts of food waste and greater amounts of wasted irrigation water and pesticides, but less cropland waste. This is largely due to fruits and vegetables, which are health-promoting and require small amounts of cropland, but require substantial amounts of agricultural inputs. These results suggest that simultaneous efforts to improve diet quality and reduce food waste are necessary.

Understanding the Impacts of Food Consumer Choice and Food Policy Outcomes

The journal Applied Economics Perspectives and Policy just published a special issue in which  agricultural and applied economists provide their thoughts on how we might help tackle some of society’s most difficult problems and challenges.  I co-authored one of the articles with Jill McCluskey.  Here's the abstract:

The food consumer plays an increasingly prominent role in shaping the food and farming system. A better understanding of how public policies affect consumer choice and how those choices impact health, environment, and food security outcomes is needed. This paper addresses several key challenges we see for the future, including issues related to dietary-related diseases and the efficacy of policies designed to improve dietary choices, trust in the food system, acceptance of new food and farm technologies, environmental impacts of food consumption, preferences for increased food quality, and issues related to food safety. We also identify some research challenges and barriers that exist when studying these issues, including data quality and availability, uncertainty in the underlying biological and physical sciences, and the challenges to welfare economics that are presented by behavioral economics. We also identify the unique role that economists can play in helping address these key societal challenges.

Other contributions in the special issue include:

  • "Agricultural and Applied Economics Priorities for Solving Societal Challenges" by Jill McCluskey, Gene Nelson, and Caron Gala
  • "Economics of Sustainable Development and the Bioeconomy" by David Zilberman, Ben Gordon, Gal Hochman, Justus Wesseler
  • "Sustaining our Natural Resources in the Face of Increasing Societal Demands on Agriculture: Directions for Future Research" by Madhu Khanna, Scott Swinton, Kent D Messer
  • "Climate Change as an Agricultural Economics Research Topic" by Bruce McCarl and Tom Hertel
  • "Big Data in Agriculture: A Challenge for the Future" by Keith Coble, Ashok Mishra, Shannon Ferrell, and Terry Griffin
  • "The Economic Status of Rural America in the President Trump Era and beyond" by Stephan Goetz, Mark Partridge, Heather Stephens
  • "Food Insecurity Research in the United States: Where We Have Been and Where We Need to Go" by Craig Gundersen and James Ziliak
  • "The Farm Economy: Future Research and Education Priorities" by Allen Featherstone
  • "A Research Agenda for International Agricultural Trade" by Will Martin
  • "Energy Economics" by Wally Tyner, and Nisal Herath

Inequalities of Fat Taxes and Thin Subsidies

I was excited to see The Economist ran an article on my paper with Laurent Muller, Anne Lacroix, and Bernard Ruffieux, which appeared in the Economic Journal.  In typical Economist fashion, they didn't mention us by name, but here's their summary of our findings:

The study found that the taxes and subsidies actually widened health and fiscal inequalities. Fat taxes meant the women on lower incomes paid disproportionately more for food—their habits changed less. They preferred to buy food they liked rather than what made nutritional sense. Taxing the food they eat most made the poor poorer.

Subsidies encouraged all income groups to buy more fruit and vegetables. But those on higher incomes proved more responsive and so benefited most. Interestingly, richer folk were also more likely to buy the subsidised healthy food and then spend the savings they had accrued on yet more healthy food. But poorer women, if they responded to lower prices, often used the money saved to buy unhealthy items or something else entirely. Once the nutritional price policies were applied, the average share of budget spent on healthy food actually increased for the better-off.

Does a Good Diet Guarantee Good Health?

To be sure, dietary factors contribute to bad health at least some of the time for some people.  But, how large a role does diet play?  Stated differently: even if you eat well all the time, are you guaranteed to be free of cancer, heart disease, and diabetes?  Far from it according to two recent studies.  

The first was published Friday in Science by Tomasetti, Li, and Vogelstein, who investigated cancer causes.  When discussing the things that can cause cancer, causes normally fall into one of two broad categories: nature (environmental factors) or nurture (inherited genetic factors).  These authors, however, point to a third factor: as we grow, our cells naturally replicate themselves, and in the process, unavoidable DNA replication errors occur which ultimately lead to cancer.  The authors calculate that these replication errors or  

mutations are responsible for two-thirds of the mutations in human cancers.

Secondly, I ran across this interesting paper published a couple weeks ago in the Journal of the American Medical Association.  The authors attempted to ferret out how many deaths from heart disease, stroke, and type 2 diabetes (what the authors call "cardiometabolic deaths") that result each year annually come about from over- or under-consumption of certain types of foods.  As this critic pointed out, it is important to note that the authors estimates are associations/correlations NOT causation.  As such, I'd suggest caution in placing too much interpretation on the impacts from different types of food.  Nonetheless, there were a couple of other less-well-publicized results which I found interesting.

First, the authors found:

In 2012, suboptimal intake of dietary factors was associated with an estimated 318 656 cardiometabolic deaths, representing 45.4% of cardiometabolic deaths.

Stated differently, 54.6% of deaths from heart disease, stroke, and type 2 diabetes seems to be caused by something other than diet.   

The other result that I found interesting from this study is that there has been a big decline in so-called cardiometabolic deaths.  The authors write:

Between 2002 and 2012, population-adjusted US cardiometabolic deaths per year decreased by 26.5%.

Some of this decline, they argue, is due to reduced sugar consumption and increased nut/seed consumption from 2002 to 2012.

Why does all this matter?  Because these statistics help us understand the impacts of dietary and lifestyle changes.  To illustrate, let's take the above cancer statistic: 66.7% of cancers are caused by unavoidable replication errors. That leaves 33.3% of cancers, some of which are diet and lifestyle related and some of which are caused by inherited genetic factors.  For sake of simplicity, lets say you have zero risk from inherited genetic factors. Also note that the National Cancer Institute suggests that the chances of getting a new cancer in a given year are 454.8 per 100,000 people (or a 0.45% chance).  

Putting it all together, your chance of getting cancer from random errors in DNA replication is 0.667*0.45%=0.30%, and your chance of getting cancer from diet and lifestyle factors (assuming no inherited risks) is 0.333*0.45%=0.15%.  So, even if you could completely eliminate the cancer risk from diet and lifestyle factors, you'd go from a 0.45% chance of getting a new cancer to a 0.30% chance, a reduction of 0.15 percentage points.

What do school children want to eat?

In the past I have, at times, been somewhat critical of the National School Lunch Program (NSLP) guidelines destined to make school lunches healthier by reducing calories, sodium content, saturated fat, etc.  It's not not that I'm against healthy kids!  Rather, I bristled at the idea of a bunch of nutritionists, policy makers, etc. setting rules and guidelines for how they think kids should eat without considering how the children would respond to the rules.  Nutritional content is but one of the components we care about when eating - don't we also care about how the food tastes, how much it costs, whether it leaves feeling full, whether it is safe to eat, etc. etc.  In short, the guidelines were established with limited understanding of what children want to eat, and as such we knew very little about whether the rules might increase food waste, increase the frequency of home lunches, cause unintended substitution patterns, and so on.  

In an interesting paper in the most recent edition of the American Journal of Agricultural Economics, a team of six researchers sought to do what should have been done prior to implementing nutritional guidelines.  In particular, the authors studied almost 280,000 school lunch choices of about 5,500 elementary age children in a suburban South Carolina school district.  The authors know the precise foods available at each lunch offering, the nutritional characteristics of the foods, which foods the child selected (or whether the child brought a lunch from home - note that lunch menus were published well in advance), and some of the characteristics of the child who made the choice such as their grade, gender, race, and whether they received free or reduced price lunch.

The authors are able to take all this data to estimate demand curves associated with different food offerings.  Their demand models let them answer questions like the following:

  • If the sodium content of a pizza offering were lowered, how would that change the number of children who select it?  
  • If a low fat pizza is paired with a peanut butter sandwich, which would most people choose?
  • If the caloric content were unilaterally lowered on all offerings, how many more children would bring their lunches from home?       

Here's what the authors find:

If the protein content of Entrée 1 is increased by 3.2grams (one standard deviation of all entree offerings over the course of study), students are, on average, 2.8 percentage points more likely to select that offering. Increasing the fat content of Entrée 1 by one standard deviation (3.9grams) has a similar effect, though smaller in magnitude; students are only 0.2 percentage points more likely to select Entrée 1 because of this increase in its fat content. Increasing the carbohydrate content has the opposite effect; the average probability of choosing Entrée 1 over the alternatives decreases by 3 percentage points if the carbohydrate content increased by 6.8grams (one standard deviation). Thus, the first row of table 3 reveals that students prefer more fat and protein but dislike additional carbohydrates. While the results for sodium are positive, the effect is not statistically significant.

There are important differences across children:

While an increase in the fat content of Entrée 1 increases the average probability that a student receiving free lunch will select it, the same increase in fat reduces the likelihood a student who pays full-price will select Entrée 1. The results also suggest that students who pay full-price are more likely to select offerings with more protein than students receiving free or reduced-price lunches (Bonferroni p-value <0.0001), and those who received free lunches are more likely to reject entrées with additional sodium relative to students who pay full-price or students who received reduced-price lunches (Bonferroni p-value =0.0044).

The authors use their results to suggest how "schools can increase the healthfulness of their students’ meals by replacing unhealthy options with relatively healthy options that are already popular amongst the students."  One things the authors didn't do (but which is possible given their estimates) is to ask: are the children better or worse off (at least as measured by their own preferences revealed by their short run choice behavior) with the new nutritional standards?  Which types of children are now happier or sadder?  Because there is no price variation in the dataset, the authors can't provide a monetary measure of the loss (or gain) in student happiness, but they could covert it to some other unit they measure - such as grams of protein or calories.  

Nonetheless, this is a really interesting study, and it has a number of important findings.  Here's some from the conclusions:

Nationwide between school year 2010–11 and 2012–13, the number of students receiving free lunches increased while the number of students purchasing full-price lunches decreased, leading to an overall reduction in participation by 3.7% (Government Accounting Office 2014). The results of our analyses suggest that the underlying preferences for offerings with higher levels of fat and lower levels of carbohydrates may be driving the decline in NSLP participation. Full-price participants are most likely to respond to changes in the nutritional content of the offered entrées by opting out of purchasing a school lunch altogether. Our findings have particularly important implications for the NSLP’s stated goal of reducing childhood obesity as they indicate that children are likely to reject those entrées that are most compatible with this particular aim. However, our results do suggest that the future guidelines reducing sodium levels may not trigger additional participation declines.